1. Field of the Invention
This invention relates to dispensing systems and more particularly to small quantity discreet dot dispensing systems employing needle-like dispensing tips.
2. Description of Related Art
Ultra small quantity dispensing devices utilizing needle-like dispensing tips to dispense discreet drops, one at a time, are known. Such structures may employ axially movable pistons aligned with an axial bore or lumen in the dispensing tip which defines a dispensing orifice at an axial end thereof. The movement of the piston is controlled to dispense minute quantities onto a workpiece at a determined position. Such devices are shown, for example, in U.S. Pat. Nos. 4,572,103 and 4,941,428, the teachings of which are herein incorporated by reference.
A common difficulty associated with such drop at a time dispensers is the phenomenon known as wicking, or wetting, where the material being dispensed, instead of forming a discreet neat drop at the tip end, flows backwardly along the outside of the tip. This phenomenon is related to the viscosity of the material and materials having a low viscosity, and/or low surface tension, exhibit a greater tendency to wet the nozzle tip. When this occurs consistent repetitive volumetric controlled dispensing may be adversely impacted.
It would therefor be an advance in the art to provide a minute quantity discreetxe2x80x94drop dispenser employing a needle-like dispense tip which has a configuration to minimizing tip wicking.
It would be further an advance in the art to provide a minute quantity discreet drop dispensing tip which reduces tip wetting and enhances drop geometry formation and drop volume consistency.
These and other improvements are obtained by the following described invention.
A small volume dispense pump assembly is provided with a hollow dispense tip defining a dispense orifice at an axial end of the tip. In a preferred embodiment the tip is provided with a diameter increasing bore configuration adjacent the dispense orifice end of the tip. The diameter increase may be provided by a frustoconical inner diameter chamfer at the dispense end extending from the nozzle lumen inner diameter to approximately the tip""s outer diameter.
In addition to enhancing the geometry of the tip""s orifice, the tip may be provided with an interior wicking wire extending lengthwise of the lumen, at least at the dispense end portion and preferably projecting beyond the dispensing end of the tip. The wicking wire, preferably positioned centrally of the bore, may be attached to the tip for movement therewith or may be independent of the tip and moveable with respect to the tip. The provision of a wicking wire assists in reducing exterior flow of the fluid being dispensed upwardly along the outer diameter of the nozzle tip as the material tends to flow along the wire.
In an embodiment of the invention an enlarged inner diameter interior dimensions at the orifice of the nozzle tip permits the formation of a drop partially interially of the nozzle tip and partially externally beyond the tip end.
In an embodiment, the provision of an inner diameter enlarged area adjacent the tip orifice is combined with a wicking wire projecting into the enlarged diameter area.
In an embodiment a frustoconical inner diameter enlarging area is provided adjacent the tip orifice and a wicking wire extends axially of the nozzle tip extending into the frustoconical area.
In a further embodiment of the invention a nozzle tip frustoconical inner diameter increasing area is provided in the tip adjacent the orifice communicating to a tip lumen with a wicking wire axially positioned in the tip lumen and projecting through the frustoconical area terminating axially beyond the end of the tip.
It is therefore an object of the invention to provide an improved nozzle tip for minute quantity drop dispensing.
It is further an object of this invention to reduce nozzle tip outer diameter wicking in minute quantity drop dispensers.
It is another, and more particular, object of this invention to improve discrete dot dispensing utilizing needle-like dispensing nozzle tips by providing a tip lumen inner diameter increase adjacent the orifice of the nozzle tip.
It is another and more particular object of this invention to improve dot dispensing in minute quantity dispensers employing needle-like dispense tips by providing a frustoconical inner diameter lumen increase adjacent the orifice of the tip and by further providing a wicking wire positioned interior of the tip extending into the frustoconical area whereby tip outer diameter wicking is minimized.
These and other objects of this invention will become apparent to those skilled in the art from the following detail description of one preferred embodiments, it being understood that many variations will be apparent to those of ordinary skill in the art in substitution for the specific structures disclosed in the preferred embodiment.